Amplitude and phase matching for layered modulation reception

ABSTRACT

An apparatus and method for receiving layered modulation signals is disclosed. A typical method includes receiving a layered modulation signal including an upper layer signal and a lower layer signal, demodulating and decoding the upper layer signal from the received layered modulation signal, estimating an upper layer amplitude factor and an upper layer phase factor from the received layered modulation signal. A substantially ideal upper layer signal is reconstructed from the demodulated and decoded upper layer signal including matching an ideal amplitude and an ideal phase by applying the upper layer amplitude factor and the upper layer phase factor to the reconstructed ideal upper layer signal. Finally, the reconstructed ideal upper layer signal is subtracted from the received layered modulation signal to produce the lower layer signal for processing.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part application and claims the benefit under35 U.S.C. Section 120 of the following co-pending and commonly-assignedU.S. utility patent application, which is incorporated by referenceherein:

Utility application Ser. No. 09/844,401, filed Apr. 27, 2001, by ErnestC. Chen, entitled “LAYERED MODULATION FOR DIGITAL SIGNALS,” attorneys'docket number PD-200181 (109.51-US-01).

This application claims the benefit under 35 U.S.C. §119(e) of thefollowing U.S. Provisional Patent Application, which is incorporated byreference herein:

Application Ser. No. 60/421,332, filed Oct. 25, 2002, by Ernest C. Chen,Jeng-Hong Chen, Kenneth Shum and Joungheon Oh, entitled “AMPLITUDE ANDPHASE MATCHING FOR LAYERED MODULATION RECEPTION,” attorneys' docketnumber PD-201033 (109.73-US-P1).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to systems and methods for receivinglayered modulation signals, particularly in a direct satellite broadcastsystem.

2. Description of the Related Art

Digital signal communication systems have been used in various fields,including digital TV signal transmission, either terrestrial orsatellite. As the various digital signal communication systems andservices evolve, there is a burgeoning demand for increased datathroughput and added services.

It has been proposed that a layered modulation signal, transmittingcoherently or non-coherently both upper and lower layer signals, can beemployed to meet these needs and more. Such layered modulation systemsallow higher information throughput, with and without backwardcompatibility. When backward compatibility is not required (such as withan entirely new system), layered modulation can still be advantageousbecause it requires a TWTA peak power significantly lower than that fora conventional 8PSK or 16QAM modulation format for a given throughput.

However, to receive such layered modulation signals requiresreconstruction of the upper layer signals to remove them from the totalsignal for lower layer signal processing to occur. Further, theperformance of lower layer demodulation depends on the cancellationaccuracy. The reconstructed signal should optimally match the receivedsignal in overall amplitude and phase. Therefore, amplitude and phaseerrors in the reconstructed signal at the point of signal cancellationneed to be estimated.

Accordingly, there is a need for systems and methods for amplitude andphase matching of the received signal with the reconstructed signal in acommunication system using layered modulation. The present inventionmeets these needs.

SUMMARY OF THE INVENTION

Layered modulation reconstructs the upper layer signal and removes itfrom the received signal to leave a lower layer signal. Lower layersignal demodulation performance requires good signal cancellation, whichin turn requires the reconstructed signal to include accurate amplitudeand phase effects from signal propagation path, filters and low noiseblock (LNB). Values of these parameters may change from receiver toreceiver and therefore must be estimated at each receiver.

Embodiments of the invention utilize a technique to estimate themultiplicative relationship of magnitude and phase components betweenreceived and synthesized upper layer signals. These attributes will bemultiplied to the signal synthesized from the satellite response, knowntransmitter and receiver filter characteristics, and estimatednarrowband phase noise without additive white Gaussian noise (AWGN). Theresult of this multiplication is a high-fidelity representation of theupper layer signal which greatly enhances the cancellation performance.In addition, the required computational processing to implement theinvention is minimal.

A typical method of the invention includes receiving a layeredmodulation signal including an upper layer signal and a lower layersignal in noise and interference, demodulating and decoding the upperlayer signal from the received signal, estimating an upper layeramplitude factor and an upper layer phase factor from the receivedlayered modulation signal. A substantially ideal upper layer signal isreconstructed from the demodulated and decoded upper layer signalincluding matching an ideal amplitude and an ideal phase by respectivelyapplying the upper layer amplitude factor and the upper layer phasefactor to the reconstructed ideal upper layer signal. Finally, thereconstructed ideal upper layer signal is subtracted from the receivedsignal to produce the lower layer signal for processing.

A typical apparatus of the invention includes a signal processor fordemodulating and decoding an upper layer signal from a received layeredmodulation signal wherein the received signal includes the upper layersignal and a lower layer signal in noise and interference. An estimatorprovides an estimate of an upper layer amplitude factor and an upperlayer phase factor from the received layered modulation signal. Asynthesizer reconstructs a substantially ideal upper layer signal fromthe demodulated and decoded upper layer signal including matching anideal amplitude and an ideal phase by respectively applying the upperlayer amplitude factor and the upper layer phase factor to thereconstructed ideal upper layer signal. Finally, the lower layer signalis produced for processing by subtracting the reconstructed ideal upperlayer signal from the received layered modulation signal with asubtractor.

Typically, the received layered modulation signal is a multiple phaseshift keyed (PSK) signal in each layer and can comprise separatenon-coherent modulated signal layers. Embodiments of the invention canestimate the upper layer phase factor from a mean vector of adistribution of one or more constellation nodes of the upper layersignal from the received layered modulation signal. The upper layerphase and amplitude factors can be estimated from a plurality ofconstellation nodes of the upper layer signal.

Furthermore, a transmission characteristic map can also be applied toimprove the estimates of the upper layer amplitude and phase factors.The transmission characteristic map can comprise AM-AM maps and AM-PMmaps characterizing effects of the transmission path. For example, thetransmission characteristic map can represent a non-linear distortionmap of amplifier characteristics of the transmission path, such as theeffect of a travelling wave tube amplifier (TWTA) in a satellitetransmission path.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings in which like reference numbers representcorresponding parts throughout:

FIGS. 1A-1C illustrate a layered modulation signal constellation for anexemplary QPSK signal format;

FIGS. 2A and 2B illustrate a signal constellation of a secondtransmission layer over the first transmission layer before and afterfirst layer demodulation;

FIG. 3 is a block diagram for a typical system implementation of thepresent invention;

FIGS. 4A and 4B illustrate the problem and the solution, respectively,using QPSK as an example;

FIG. 5 is an overview of the layered modulation reception processincluding the legacy receiver processes;

FIG. 6 is a flowchart of the signal cancellation process; and

FIGS. 7A and 7B illustrate a general solution for amplitude and phasematching between received and reconstructed signals.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the following description of the preferred embodiment, reference ismade to the accompanying drawings which form a part hereof, and in whichis shown by way of illustration a specific embodiment in which theinvention may be practiced. It is to be understood that otherembodiments may be utilized and structural changes may be made withoutdeparting from the scope of the present invention.

1. Overview

FIGS. 1A-1C illustrate the basic relationship of signal layers in anexemplary layered modulation transmission. FIG. 1A illustrates a firstlayer signal constellation 100 of a transmission signal showing thesignal points or symbols 102. FIG. 1B illustrates the second layersignal constellation of symbols 104 over the first layer signalconstellation 100 when the layers are coherent. FIG. 1C illustrates asecond signal layer 106 of a second transmission layer over the firstlayer constellation where the layers are non-coherent. The second layer106 rotates about the first layer constellation 102 due to the relativemodulating frequencies of the two layers in a non-coherent transmission.Both the first and second layers rotate about the origin due to thefirst layer modulation frequency as described by path 108.

FIGS. 2A-2B illustrate a signal constellation of a second transmissionlayer over the first transmission layer. FIG. 2A shows the constellation200 before the first carrier recovery loop (CRL) and FIG. 2B shows theconstellation 200 after CRL. In this case, the signal points of thesecond layer are actually rings 202. Relative modulating frequenciescause the second layer constellation to rotate around the nodes of thefirst layer constellation. After the second layer CRL this rotation iseliminated The radius of the second layer constellation is determined byits power level. The thickness of the rings 202 is determined by thecarrier to noise ratio (CNR) of the second layer. As the two layers arenon-coherent, the second layer may be used to transmit analog or digitalsignals.

FIG. 3 is a block diagram for a typical system 300 implementation of thepresent invention. Separate transmitters 316A, 316B, as may be locatedon any suitable platforms, such as satellites 306A, 306B, are used tonon-coherently transmit different layers of a signal of the presentinvention. Uplink signals are typically transmitted to each satellite306A, 306B from one or more transmit stations 304 via an antenna 302.The layered signals 308A, 308B (downlink signals) are received atreceiver antennas 312, 320, such as satellite dishes, each with a lownoise block (LNB) 310, 318 where they are then coupled to integratedreceiver/decoders (IRDs) 314, 322. Because the signal layers may betransmitted non-coherently, separate transmission layers may be added atany time using different satellites 306A, 306B or other suitableplatforms, such as ground based or high altitude platforms. Thus, anycomposite signal, including new additional signal layers will bebackwards compatible with legacy receivers which will disregard the newsignal layers. Of course, non-backwards compatible applications are alsopossible in which both IRDs 314 and 322 are layered modulation IRDs,capable of receiving more than one signal layer. To ensure that thesignals do not interfere, the combined signal and noise level for thelower layer must be at or below an allowed threshold level for the upperlayer.

To receive layered modulation signals the upper layer signals must bereconstructed to cancel them from the total signal for lower layersignal processing to occur. Further, the performance of lower layerdemodulation depends on the signal cancellation accuracy. Thereconstructed signal should optimally match the received signal inoverall amplitude and phase. Therefore, amplitude and phase errors inthe reconstructed signal at the point of signal cancellation need to beestimated. The core of this invention includes techniques to optimallyestimate a relative amplitude and phase between the received andreconstructed signals.

2. Amplitude and Phase Matching

FIG. 4A illustrates the problem which requires amplitude and phasematching, using QPSK as an example. FIG. 4A illustrates the QPSKconstellation 400 before constellation amplitude and node phasecompensation. All of the four triangles 402 (defining the phase error,θ_(e)) are identical. Embodiments of the invention can be applied toother modulation formats as well, such as 8PSK and 16QAM. The four nodes404, represented by circles in FIG. 4A are ideal symbol locations afterupper layer demodulation. They have a reference magnitude of one andrespective phase angles of π/4, 3π/4, 5π/4, and 7π/4. However, in realapplications before they are converted by the analog to digital (A/D)converter at the receiver, the ideal symbol nodes 404 will have shiftedin magnitude and phase with uncompensated and uncalibrated factors asrepresented by the actual nodes 406. FIG. 4B illustrates the collapsedideal nodes 404 and the actual nodes 406.

The uncalibrated power represents an unknown magnitude scaling factor tothe signal into the receiver (e.g., the set-top box). The low noiseblock (LNB), filters and other factors prior to the receiver typicallyintroduce a phase distortion factor. These distortions should beincluded in the reconstructed upper layer signal to improve signalcancellation performance. As described above, FIG. 4A models theseunknown distortions. The magnitudes of the received nodes for the upperlayer signal are different from the assumed value of one, and aremodeled by a relatively constant but unknown scaling factor, a_(e). Thereceived nodes for the upper layer signal are also offset from the idealnodes by an equal but unknown phase adjustment amount, the phase error,θ_(e). The signal is also corrupted with noise, interference and asecond signal, represented by concentric circles around the nodes inFIGS. 4A and 4B. However, knowledge of each symbol node of the QPSKupper layer signal is available from forward error correction (FEC)decoding.

3. Exemplary Receiver Embodiment

FIG. 5 is a block diagram of the layered modulation reception apparatus.As shown, a receiver or integrated receiver/decoder (IRD) 500 embodimentof the invention estimates the upper layer power and phase which is usedto re-scale the re-modulated signal, before the signal is subtractedfrom the received signal to leave only the lower layer signal. Thesignal 502 is received and the upper layer is demodulated by thedemodulator 504. The demodulated signal 506 is then decoded (e.g.,forward error correction decoding) by the decoder 508 to produce symbols510 which are then communicated to the upper layer transport 512 forfurther processing and presentation to a viewer. The demodulator 504 anddecoder 508 can be referred to in combination as a signal processor forprocessing the received signal. The foregoing processes encompass thefunctions of a legacy receiver decoding only the upper layer of theincoming signal 502 in cases of backwards compatible applications.

The lower layer of the incoming signal 502 requires further processingto decode. An ideal upper layer signal is generated by a synthesizer orremodulator 514. The remodulator 514 receives the upper layer timing andcarrier 516 from the upper layer demodulator 504 and the upper layersymbols 510 output from the decoder 508. To enhance production of theideal upper layer signal, the remodulator 514 can also receive inputfrom a pulse shaping filter 518 and a non-linear distortion map 520(which models transmission characteristics applied to the signal byelements such as the travelling wave tube amplifiers [TWTA] of thesatellite).

A key element of the present invention comprises an estimator 522 whichreceives the incoming signal 502 and estimates an upper layer amplitudeand phase factor. The factor is supplied to the remodulator 514 tofurther improve accurate reproduction of the ideal upper layer signaland benefit recovery of the lower layer.

The ideal upper layer signal is communicated to a subtractor 524 whereit is subtracted from the incoming signal 502 which has beenappropriately delayed by a delay function 526 to account for theprocessing time of the upper layer demodulator 504 and the remodulator514. The output of the subtractor 524 is the lower layer signal which iscommunicated to the lower layer demodulator 528 and decoder 530 toproduce the lower layer symbol output 532 which is ready to be processedby the lower layer transport for presentation.

4. Amplitude and Phase Matching for Constant-Envelope Signals

FIG. 6 is a flowchart of the signal cancellation process 600. As thereceived signal enters into the IRD 502 at block 602, the upper layersignal is first demodulated and decoded as described above at block 604.Meanwhile, an ideal upper layer signal is synthesized at block 606 withthe decoded symbols 608 and other waveform parameters 610 derived fromblock 602. The synthesized signal is then mapped with TWTA AM-AM andAM-PM curves at block 612, which are positioned with a suitableoperating point estimate 614 obtained from the local upper layerdemodulator 604 or downloaded from broadcast center, shown at block 616.

Typically, the TWTA performance maps will comprise measurements of theoutput amplitude modulation versus the input amplitude modulation (theAM-AM map) and the output phase modulation versus the input amplitudemodulation (the AM-PM map). In the present invention, the receivedsignal represents the amplifier output (plus lower layer signal,interference and noise) and the generated ideal signal represents theamplifier input. The maps are used to determine the effect of the TWTAon the signal and simulate those effects in the layer subtraction toyield a more precise lower layer signal. These performance maps are usedto facilitate and/or improve reception of different layers of a systemusing a layered modulation transmission scheme.

Estimation of the operating point and AM-AM and AM-PM mapping arefurther discussed in U.S. patent application Ser. No. 10/165,710 filedJun. 7, 2002, by Ernest C. Chen and entitled “SATELLITE TWTA ON-LINENON-LINEARITY MEASUREMENT”, and Utility application Ser. No. 09/844,401,filed Apr. 27, 2001, by Ernest C. Chen, entitled “LAYERED MODULATION FORDIGITAL SIGNALS,” which are both incorporated by reference herein.

The TWTA-mapped signal and the received signal are used to estimate theoverall amplitude and phase factors in block 618. The mapped TWTA signalis then matched to the received signal in amplitude and phase at block620. Finally, the corrected signal is subtracted at block 622 from thereceived signal, which has been properly delayed for timing alignment atblock 624, to reveal the lower layer signal at block 626.

The key process of the present invention lies in referencing thereceived signal to the reconstructed signal, as in blocks 618 and 620.Referring back to FIG. 4A, a ratio is formed between the received signaland its decoded node signal. FIG. 4B shows the distribution of thesecomplex ratios in effective additive noise; division by the decoded nodesignal collapses the received signals from all QPSK nodes to a singlenode near the horizontal axis. The mean of this distribution is thecenter of the concentric circles that represent the noise distribution.The mean vector is the estimate for signal matching purposes. Theestimate vector consists of an amplitude, aαe, and phase, θ_(e). Themathematical derivation is shown as follows.

-   r_(i) is the received signal for the i-th upper layer symbol in an    effective noise;-   n_(i) is the effective noise associated with r_(i);-   θ_((i)) is the decoded phase for the i-th symbol;-   N_(s) is the number of signal symbols processed;-   aαe is the amplitude scale error to be estimated; θ_(e) is the    angular error to be estimated; and    $\theta_{(i)} \in \left\{ {\frac{\pi}{4},\frac{3\pi}{4},\frac{5\pi}{4},\frac{7\pi}{4}} \right\}$    for QPSK. Other modulation forms may be processed with a generalized    solution discussed in the next section.    The received signal after carrier recovery can be modeled as:    r _(i)=a_(e) exp(j(θ_((i))+θ_(e)))+n _(i), where i=1, . . . ,    N_(s)  (1)    Removing the decoded symbol phase yields: $\begin{matrix}    {{{r_{i}^{\prime} \equiv \frac{r_{i}}{\exp\left( {j\theta}_{(i)} \right)}} = {{a_{e}{\exp\left( {j\theta}_{e} \right)}} + n_{i}^{\prime}}};} & (2)    \end{matrix}$    where    $n_{i}^{\prime} = {\frac{n_{i}}{\exp\left( {j\theta}_{(i)} \right)}.}$    n_(i) and n′_(i) have zero mean and the same variance. The estimated    complex amplitude and phase scale factor is formed by averaging over    r′_(i) as follows. $\begin{matrix}    {{r_{0} \equiv {{avg}\left\{ r_{i}^{\prime} \right\}}} = {\frac{\sum\limits_{i = 1}^{N_{s}}r_{i}^{\prime}}{N_{s}} \equiv {\hat{a}\quad{{\exp\left( {j{\hat{\theta}}_{e}} \right)}.}}}} & (3)    \end{matrix}$    The amplitude and phase error estimates are:    {circumflex over (α)} _(e)=abs(r ₀); and  (4)    {circumflex over (θ)}_(e)=angle(r ₀)  (5)

The preceding analysis shows that the estimated residual phase{circumflex over (θ)}_(e) will be zero if the signal phase has beenprecisely followed with carrier recovery loop, etc. {circumflex over(θ)}_(e) “sweeps up” residual phase errors due to carrier recoveryinaccuracy and other errors.

As shown by amplitude and phase matching 620 operation in FIG. 6, theestimated amplitude and phase factors form a complex multiplier to thereconstructed signal for subtraction from the delayered received signalto optimally reveal the lower layer signal.

5. Amplitude and Phase Matching for General Signals

FIGS. 7A and 7B illustrate a general solution for amplitude and phasematching between received and reconstructed signals that are notrestricted to QPSK. As shown in FIG. 7A, all triangles 702 are similarwith ratios a₁, a₂, . . . a_(k), etc. Thus, the technique, describedabove with respect to QPSK, can be easily extended for use with areconstructed signal which varies in amplitude due to unequal signalnode amplitudes, variations due to inter-symbol interference prior tomatched filtering, satellite non-linear response, etc. The reconstructedsignals are shown collapsed in FIG. 7B after node phase compensationwith unequal amplitudes between ideal nodes 704A and 704B as well astheir respective received nodes 706A and 706B.

A general analysis for amplitude and phase matching of the presentinvention follows. This analysis degenerates to the preceding analysiswhen applied to a QPSK constellation which has identical magnitudes(amplitudes). For a general layered communication signal, theconstellation symbols may utilize different amplitudes and phases. Thus,

-   aα(i) is the amplitude of the i-th symbol over time;-   θ_((i)) is the phase of the i-th symbol over time; and    s _((i))=a_((i)) exp(jθ_((i)))      The received signal after the carrier recovery loop can be modeled    as:    r _(i)=a_(e)a_((i)) exp(j(θ_((i))+θ_(e)))+n_(i), where i=1, . . . ,    N_(s)  (6)    Removing the remodulated and re-encoded signal phase and weighting    by the signal magnitude, similar to matched-filtering forms:    $\begin{matrix}    {{r_{i}^{\prime} = {\frac{a_{(i)}r_{i}}{\exp\left( {j\theta}_{(i)} \right)} = {{a_{e}a_{(i)}^{2}{\exp\left( {j\theta}_{e} \right)}} + n_{i}^{\prime}}}}{{{where}\quad n_{i}^{\prime}} = \frac{a_{(i)}n_{i}}{\exp\left( {j\theta}_{(i)} \right)}}} & (7)    \end{matrix}$    and n_(i) and n′_(i) have zero mean. The estimated complex amplitude    and phase scale factor is formed by summing over r′_(i), normalized    by the sum of the ideal powers as follows. $\begin{matrix}    {r_{0} \equiv \frac{\sum\limits_{i = 1}^{N_{s}}r_{i}^{\prime}}{\sum\limits_{i = 1}^{N_{s}}a_{i}^{2}} \equiv {{\hat{a}}_{e}{{\exp\left( {j{\hat{\theta}}_{e}} \right)}.}}} & (8)    \end{matrix}$    As before, the amplitude and phase error estimates are:    {circumflex over (α)}_(e) =abs(r ₀); and  (9)    {circumflex over (θ)}_(e)=angle(r ₀)  (10)    Note that equation (8) reduces to equation (3) when all a_((i)) are    equal. However, the general solution of equation (8) may be    preferred even for nPSK signals since all received signal symbols    have non-constant amplitudes prior to receiver matched filtering.    6. Alternative General Analysis for Amplitude and Phase Matching

An alternative approach to the problem, which results in the samesolution as the preceding general solution can be found through vectoranalysis. The approach begins with the same mathematical model, but usescomplex numbers to represent phases and magnitudes of the receivedsymbols.

The problem is characterized in terms of a minimization process. SupposeR is the received signal vector and X is the reconstructed signalvector; the vectors consist of the associated time samples as theircomponents. Both are column vectors with length N_(s), where N_(s) isthe number of data symbols to be processed. A complex scalar factor z isto be estimated for multiplication to X later. The estimate is chosen tominimize the difference between R and z_(X), or specifically, thenorm-squared error: (R−z_(X))^(H)(R−z_(X)), where ( )^(H) is theHermitian operator. The result is a least-square-error (LSE) solution:$\begin{matrix}{z_{LS} = \frac{{\underset{\_}{X}}^{H}\underset{\_}{R}}{{\underset{\_}{X}}^{H}\underset{\_}{X}}} & (11)\end{matrix}$X^(H)X is a scalar equal to the power of the reconstructed signal.z_(LS) is the complex correlation between received signal vector X andreconstructed signal vector R, normalized by X^(H)X. Thus, z_(LS) is thecomplex correlation of the received signal vector and the reconstructedsignal vector and normalized by a power of the reconstructed signalvector, identical to the previous solution expressed by equation (8).

This concludes the description including the preferred embodiments ofthe present invention. The foregoing description of the preferredembodiment of the invention has been presented for the purposes ofillustration and description. It is not intended to be exhaustive or tolimit the invention to the precise form disclosed. Many modificationsand variations are possible in light of the above teaching.

It is intended that the scope of the invention be limited not by thisdetailed description, but rather by the claims appended hereto. Theabove specification, examples and data provide a complete description ofthe manufacture and use of the apparatus and method of the invention.Since many embodiments of the invention can be made without departingfrom the scope of the invention, the invention resides in the claimshereinafter appended.

1-10. (canceled)
 11. A method of receiving layered modulation signals,comprising: receiving a layered modulation signal including an upperlayer signal and a lower layer signal; demodulating and decoding theupper layer signal from the received layered modulation signal;estimating an upper layer amplitude factor and an upper layer phasefactor from the received layered modulation signal; reconstructing asubstantially ideal upper layer signal from the demodulated and decodedupper layer signal including matching an ideal amplitude and an idealphase by applying the upper layer amplitude factor and the upper layerphase factor to the reconstructed ideal upper layer signal; subtractingthe reconstructed ideal upper layer signal from the received layeredmodulation signal to produce the lower layer signal for processing. 12.The method of claim 11, wherein the layered modulation signal comprisesseparate non-coherent modulated signal layers.
 13. The method of claim11, wherein the layered modulation signal comprises a layered multiplephase shift keyed (PSK) signal.
 14. The method of claim 11, wherein theupper layer phase factor and the upper layer amplitude factor arecombined to form a complex multiplying factor, which is the complexcorrelation of a received signal vector and a reconstructed signalvector and normalized by a power of the reconstructed signal vector. 15.The method of claim 14, wherein the complex multiplying factor ismathematically expressed by z_(LS)=(X^(H)X)⁻¹X^(H)R, where R is thereceived signal vector and X is the reconstructed signal vector.
 16. Themethod of claim 11, wherein the upper layer phase factor is estimatedfrom a mean vector of a distribution of the received layered modulationsignal relative to one or more nodes of the upper layer signal.
 17. Themethod of claim 11, wherein the upper layer phase factor is estimatedfor a plurality of nodes of the upper layer signal in combination. 18.The method of claim 11, wherein the upper layer amplitude factor isestimated from a mean vector of a distribution of the received layeredmodulation signal relative to one or more nodes of the upper layersignal.
 19. The method of claim 11, wherein the upper layer amplitudefactor is estimated for a plurality of nodes of the upper layer signalin combination.
 20. The method of claim 11, wherein the upper layeramplitude factor is estimated separately for one or more of a pluralityof nodes of the upper layer signal.
 21. The method of claim 11, whereinthe upper layer amplitude factor and the upper layer phase factor arefurther estimated from a transmission characteristic map.
 22. The methodof claim 21, wherein the transmission characteristic map represents anon-linear distortion map of an amplifier characteristic of thetransmission path.
 23. The method of claim 21, wherein the transmissioncharacteristic map comprises an AM-AM map.
 24. The method of claim 21,wherein the transmission characteristic map comprises an AM-PM map. 25.An apparatus for receiving layered modulation signals, comprising: asignal processor for demodulating and decoding an upper layer signalfrom a received layered modulation signal wherein the received signalincludes the upper layer signal and a lower layer signal; an estimatorfor estimating an upper layer amplitude factor and an upper layer phasefactor from the received layered modulation signal; a synthesizer forreconstructing a substantially ideal upper layer signal from thedemodulated and decoded upper layer signal including matching an idealamplitude and an ideal phase by applying the upper layer amplitudefactor and the upper layer phase factor to the reconstructed ideal upperlayer signal; and a subtractor for subtracting the reconstructed idealupper layer signal from the received layered modulation signal toproduce the lower layer signal for processing.
 26. The apparatus ofclaim 25, wherein the layered modulation signal comprises separatenon-coherent modulated signal layers.
 27. The apparatus of claim 25,wherein the layered modulation signal comprises a layered multiple phaseshift keyed (PSK) signal.
 28. The apparatus of claim 25, wherein theupper layer phase factor and the upper layer amplitude factor arecombined in a complex multiplying factor, which is the complexcorrelation of a received signal vector and a reconstructed signalvector and normalized by a power of the reconstructed signal vector. 29.The apparatus of claim 28, wherein the complex multiplying factor ismathematically expressed by z_(LS)=(X^(H)X)⁻X^(H)R, where R is areceived signal vector and X is a reconstructed signal vector.
 30. Theapparatus of claim 25, wherein the upper layer phase factor is estimatedfrom a mean vector of a distribution of the received layered modulationsignal relative to one or more nodes of the upper layer signal.
 31. Theapparatus of claim 25, wherein the upper layer phase factor is estimatedfor a plurality of nodes of the upper layer signal in combination. 32.The apparatus of claim 25, wherein the upper layer amplitude factor isestimated from a mean vector of a distribution of the received layeredmodulation signal relative to one or more nodes of the upper layersignal.
 33. The apparatus of claim 25, wherein the upper layer amplitudefactor is estimated for a plurality of nodes of the upper layer signalin combination.
 34. The apparatus of claim 25, wherein the upper layeramplitude factor is estimated separately for one or more of a pluralityof nodes of the upper layer signal.
 35. The apparatus of claim 25,wherein the upper layer amplitude factor and the upper layer phasefactor are further estimated from a transmission characteristic map. 36.The apparatus of claim 35, wherein the transmission characteristic maprepresents a non-linear distortion map of an amplifier characteristic ofthe transmission path.
 37. The apparatus of claim 35, wherein thetransmission characteristic map comprises an AM-AM map.
 38. EW) Theapparatus of claim 35, wherein the transmission characteristic mapcomprises an AM-PM map.